The mobile communication system developed for the user to communicate on the move. With the rapid advance of technologies, the mobile communication system has evolved to the level capable of providing high speed data communication service beyond the early voice-oriented services. Recently, as one of the next generation mobile communication system, Long Term Evolution-Advanced (LTE-A) is on the standardization by the 3rd Generation Partnership Project (3GPP). LTE is a technology for realizing high-speed packet-based communications with the data rate higher than the currently available data rate aims at commercial deployment around 2010 timeframe.
With the evolution of the 3GPP standard, many studies being conducted for optimization of radio networks as well as improvement of data rate. In the initial radio network configuration or optimization stage, a base station or a base station controller should collect radio environment information related to its own cell coverage, and this process is called Drive Test. The conventional drive test is very time-consuming and laborious task performed in such a way that an operator carries the test apparatuses on a vehicle while performing the measurement task repeatedly for a long time. The measurement result is used to configure the system parameters of the base stations or base station controllers. Such a conventional drive test increases total costs and time of the radio network optimization and maintenance. Study on minimization of drive tests and enhancement of radio environment analysis process and manual configuration is being conducted in the name of MDT (Minimization of Drive Test). In more detail, the terminal measures the cell information and supplementary information on the neighbor eNBs. The terminal reports the radio channel measurement information to the eNB periodically or immediately in response to a specific event or after a predetermined time has elapsed from the time point when the radio channel measurement information has been logged. At this time, the UE operation of transmitting the measured cell information and other supplementary information to the UE is referred to as MDT measurement information report. If it is in the state capable of communicating with the eNB, the terminal transmits the neighbor cell information measurement result to the eNB immediately. Otherwise, if it is not in the state capable of communicating with the eNB, the terminal retains the logged measurement information and, when it becomes possible to communicate with the eNB, transmits the retained MDT measurement report. In the following description, the radio channel information measured by the terminal and other supplementary information are referred to as MDT measurement information, and the operation transmitting the MDT measurement information from the terminal to a base station is referred to as MDT measurement information report. When reporting MDT measurement information, if it is possible to communicate with the base station, the terminal transmits the MDT measurement information immediately. Otherwise, it is impossible to communicate with the base station currently, the terminal waits until it becomes possible to communicate with the base station. The base station uses the MDT measurement information reported by the terminal for cell area optimization.
FIG. 1 is a diagram illustrating a drive text without MDT scheme and MDT execution procedure. The conventional drive test is performed in a way of measuring signal state while roaming around the service area to search for coverage holes on a vehicle carrying the measurement device. In MDT, the terminal performs this operation instead. A Network Monitoring System (NMS) 105 may instruct to perform MDT. At this time, the NSM 105 provides an Element Manager (EM) 110 with configuration information necessary for MDT. The EM 110 generates MDT configuration to an evolved Node B (eNB) 115. The eNB 115 sends a User Equipment (UE) 120 the MDT configuration information to instruct to perform MDT as denoted by reference number 125. The UE 120 performs MDT to collect MDT measurement information. The MDT information may include location and time information as well as the signal measurement information. The collected MDT measurement information is reported to the eNB 115 as denoted by reference number 130, and the eNB 115 sends the MDT measurement information to a Trace Collection Entity (TCE) 135. The TCE 135 is a server for collecting MDT measurement information.